A digital-to-analog converter (DAC) typically drives a load through an output stage that may function as a buffer between the DAC and the load to supply the drive current to the load. Additionally, the output stage may supply voltage of different ranges to the load. For example, the output of the DAC typically has a voltage range of [0, 2.5 v]. An output stage of the DAC may transform the voltage range of [0, 2.5 v] of the DAC to different voltage ranges such as ranges of [0, 5 v], [0, 10 v], [0, 20 v], [−5 v, 5 v], [−10 v, 10 v], or [−20 v, 20 v]. Those ranges that cover only positive voltages are commonly referred to as unipolar voltage ranges, and those ranges that cover both positive and negative voltages are commonly referred to as bipolar voltage ranges.
The output stage of the DAC may achieve unipolar ranges by different combinations of resistors via software controlled switches. To achieve bipolar ranges, however, the output stage of the DAC may further include an offset voltage that shifts the output into negative voltage territories. Presently, the switching between unipolar and bipolar outputs is achieved through a bypass switch which is connected between a node for the offset voltage and a ground reference. Thus, when the bypass switch is engaged for unipolar ranges, a signal at the node that provides offset voltage is directed to the ground, thus bypassing the offset voltage. When the bypass switch is disengaged, the offset voltage is kicked in so that the output stage may supply bipolar ranges.
The bypass switch is commonly implemented by using a metal-oxide-semiconductor field-effect transistor (MOSFET) device which may exhibit nonlinear resistance which varies as a function of the current passing through the MOSFET device. The nonlinear resistance of the MOSFET device in the signal path may cause the overall integral non-linearity (INL) of the DAC to suffer. Larger MOSFET devices may reduce the INL caused by the nonlinear resistance of the MOSFET device. However, larger MOSFET devices occupy larger circuit areas and may leak current at high temperatures.